You can specify a generator's distribution during its creation. As of the time of publication, the rand crate supports the ChaCha and ISAAC distributions.
This is just confusing - ChaCha and ISAAC are just another implementations of RNG, which should provide truly random source of values - e.g. they should be uniform too. However rand contains module distributions, which contains implementation for various common distributions - like normal, exponential .... Distributions implement Sample trait which can be used to get random number according to that distribution (you supply the RNG implemetation as source of randomness - so it can be ChaCha or ISAAC for instance - or OsRand).